Material misfeed detector for power press

ABSTRACT

A material misfeed detector for a power press for discontinuing the operation of the power press on the upstroke thereof when a misfeed of the material is detected, the detecting device including a nozzle for directing a jet of air to a preformed opening formed in the material and a receiver located on the other side of the material in alignment with the nozzle and receiving the air therein, wherein the receiver directs the air to a pressure switch that is responsive to a predetermined pressure thereon to continue the operation of the power press.

United States Patent 1191 Murphy, II

MATERIAL MISFEED DETECTOR FOR POWER PRESS 3,133,481 5/1964 McCormick et a1 192/128 X Primary Examiner-J. M. Meister 76 I t P t I 1 men or g xg gz digf i z g BOX Attorney-Ell1ot A. Salter et al.

Mass. 02346 [22] Filed: Oct. 18, 1971 [57] ABSTRACT A material misfeed detector for a power press for dis- [21] Appl' N05 189,873 continuing the operation of the power press on the upstroke thereof when a misfeed of the material is des2 U.S. c1 83/61, 83/63, 192/128 tected, the detecting device including a nozzle for 51 n Clm B2 7 24 1365b 25/08, B6511 25/32 recting a jet of air to a preformed opening formed in [58] Field of Search 83/63, 61; 408/7, the material and a receiver located on the other Side 0 12; 9 2 34 5 of the material in alignment with the nozzle and receiving the air therein, wherein the receiver directs 5 References Cited the air to a pressure switch that is responsive to a pre- UNITED STATES PATENTS determined pressure thereon to continue the operation of the power press. 3,160,045 12/1964 Newgard 83/63 3,513,736 5/1970 Thorman 83/63 X 9 Claims, 4 Drawing Figures 6 i RELAY 24 9 CIRCUIT EMER. BRAKE PMENTEU URI 16 I975 EMER. BRAKE 32) FIG.2

I1 l j O 0000 00 FIG.4

MATERIAL MISFEED DETECTOR FOR POWER PRESS BACKGROUND OF THE INVENTION The apparatus as embodied herein is for use in a power press automatically auomatically performs a series of work operations on a work material such as strip stock that is progressively transferred through a work station in the apparatus, a work stool such as a punch being vertically movable relative to the work material to perform the series of preselected work operations thereon.

In operation of automatic punch presses the strip stock is progressively transferred to the work station and is progressively punched to produce a work piece of preselected design. Oftentimes the material will misfeed and unless the operator has noticed the misfeed, damage to the press tool can occur.

Prior to the instant invention, various kinds of safety devices have been proposed for detecting the improper feeding or misfeed of a work material to the work station of a punch press or the like. Generally, these prior known safety devices have included a mechanical detecting or sensing means such as a finger or the like which was supposed to sense the misalignment of the work material and actuate an appropriate device for discontinuing operation of the machine. Other devices for detecting misfeeding in punch presses have also been proposed and have incorporated fluid systems that included sensors for detecting changes in pressure thereto upon misfeed of a work material to the press work station; and although these devices in theory were operable to detect misfeeding, the fluid systems incorporated therein did not function in a practical sense to immediately detect misfeeding, and further such systems incorporated relatively complicated mechanical parts and electrical circuitry that prohibitively increased the cost of the device.

SUMMARY OF THE INVENTION The present invention relates to a safety device for use in a punch press in which a series of preselected work operations are performed on a work material that is transferred through a work station in the punch press. The safety device is designed to detect a misfeed of the work material to the work station of the punch press, and thereafter is operable to discontinue the operation of the punch press ram so as to prevent damage to the work tool thereof in striking the misfedwork material. The safety device includes a nozzle that is located on one side of the work material at the work station and that discharges a jet of compressed air toward a receiver that is located on the other side of the work piece at the work station. The receiver is vertically aligned with the nozzle and normally communicates directly with the nozzle through a preformed opening in the work material to receive ajet of air after feed of the work material to the work station of the punch press. A pressure responsive device communicates with the receiver and is operable in response to a predetermined pressure exerted thereon by the compressed air directed thereto from the receiver to close a switch that is located in circuit with the operating means for the punch press. Should a misfeed of the work material occur, the preformed opening in the work material becomes misaligned with the nozzle and receiver and the jet of compressed air from the nozzle is deflected in its path through the opening in the work material to the receiver, wherein the pressure to the pressure responsive device is decreased. Thereafter, the switch opens to interrupt the operation of the operating means of the punch press. It is significant that the operation of the operating means is interrupted on the upstroke of the punch press ram and the ram is thus prevented from returning on its downstroke, whereby the tool in the punch press is prevented from striking the misfed work material. v

Accordingly, it is an object of the present invention to provide a safety device that senses the misfeed of a work material to a work station in a punch press.

Another object of the invention is to provide a material misfeed detector in a punch press that includes an air nozzle that directs a stream of compressed air through a preformed opening in a work material to a receiver, wherein the pressure of the air as received by the receiver is operative to actuate a pressure responsive device to continue the operation of the punch press; and upon misfeed of a work material to the work station, the air stream to the receiver is deflected to reduce the pressure to the pressure responsive device that is then operative to discontinue the operation of the punch press.

Still another object is to provide a safety device for use in a punch press for detecting the misfeed of a work material to the work station thereof, the safety device incorporating an air nozzle and receiver that are located on opposite sides of the work material and that are operative to detect a misfeed of the material to the work station, provision being further made for continued operation of the machine during normal feeding of the work material to the work station and when communication between the nozzle and receiver is interrupted.

Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

FIG. 1 is an elevational view with parts shown in section and in diagrammatic form of the safety device embodied herein as employed in a punch press;

FIG. 2'is an elevational view with parts shown in section of the punch press and the safety device incorporated therein and as seen at right angles with respect to the view illustrated in FIG. 1;

FIG. 3 is an enlarged sectional view taken along 3-3 in FIG. 1; and

FIG. 4 is a top plan view of an example of a work material that is fed into the punch press and showing progressive steps in the formation of an article by successive punching operations.

DESCRIPTION OF THE INVENTION Referring now to the drawings and particularly to FIG. 1, a portion of the punch press as embodied in the present invention is illustrated, and for purposes of the subject invention, the punch press which is generally indicated at 10 is shown for use with a safety device, to be described. The invention has particular application in apparatus for automatically performing a preselected work operation on a work material such as strip stock that is progressively transferred through a work station of the punch press 10. It is understood that the concept of the invention may be incorporated in other machines that perform a similar work operation and to which a work material is directed. However, since the safety device of the present invention is particularly useful with a punch press that is automatically operated and that progressively performs an operation on strip stock, the description as follows hereinafter will be directed to use of the punch press 10.

The motor and operating structure for the punch press is not illustrated in the drawings, although this is conventional structure and forms no part of the subject invention. It is understood that the operating mechanism of the punch press is interconnected to a ram 12 of conventional construction to which a subtool assembly is interconnected. The sub-tool assembly includes an upper punch block 14 with which the ram 12 engages during a punching operation. Secured to the upper punch block 14 is a backup plate 16 having a punch or tool holder 18 joined thereto. Interconnected to the upper punch block 14 through shoulder screws 20 that ride in bores 22 in the upper punch block, is a floating pressure pad 24, spring 26 being interposed between the pressure pad 24 and the tool holder 18. A base 28 is mounted on a support and is fixed in position with respect to the movable sub-tool assembly. The base 28 is shaped to cut in any particular manner to accommodate a work material; and as shown in FIG. 2, a channel 30 is formed in the base for receiving a work material that in the present invention is in the form of an elongated metal strip 12. It is understood in the operation of the punch press 10, that the ram 12 is moved downwardly in a cyclical operation to engage the upper punch block 14 thereby producing downward vertical movement of the pressure pad 24 toward the base 28. A tool 32 carried by the tool holder 18 extends through an opening in the pressure pad 24 and is brought into engagement with the work material 32 asthe ram is moved in its downward stroke toward the base 28. As previously described, the operation of the punch press 10 is conventional and the parts of the punch press illustrated and described in FIGS. 1 and 2 are also of conventional design and form no part of the present invention.

The punch press 10 progressively performs a series of punching operations on the work material 32; and after each operation, the work material is advanced so that as it is progressively transferred through the work station, a series of work operations are performed thereon so as to produce a specific configured article. As illustrated in FIG. 4, the work strip 32 is shown in blank form at the left thereof; and as the strip work material 32 is advanced along the base 28, a particular operation is performed at the various stations therein until an article, such as for example, for use in an electrical circuit is produced. It is understood that a final punching operation will be performed on the strip to cut out the article as produced by the progressive operations of the punch press.

In the feeding of the work material 32 to the work station in the punch press 10, the work material must be precisely located within the feed channel 30 of the base 28 so that as the tool 32 is driven into the work material, a precisely formed operation is achieved. Further, if the work piece is not in proper alignment, it is possible to damage the tool 32. Unless the operator is closely observing the punching operation, any misalignment of the work material 32 will not be timely detected; and consequently, it is desirable to provide a safety device for promptly detecting the misfeed or misalignment of the work material and for discontinuing operation of the press before the tool is damaged. For this purpose the present invention incorporates a safety device in the punch press to immediately detect the misfeed of the work material 32; and as illustrated in FIGS. 1, 2 and 3, the safety device includes a nozzle generally indicated at 34 that is mounted in a bore 36 formed in the pressure pad 24 of the sub-tool assembly.

As shown in FIG. 3, the nozzle 34 has a reduced passage 38 formed therein that communicates with an enlarged passage 40, the enlarged passage 40 having communication with an interior conduit 42 that, in turn, communicates with an exterior conduit or pipe 44. The pipe 44 is interconnected to a source of fluid under pressure, such as compressed air that is directed thereto through a regulator 46 and an air filter 48. It is seen that the compressed air is introduced into the interior conduit 42 and then into the passage 40 and the reduced passage 38 for ejection in ajet stream 49 downwardly toward the base 28.

Formed in the base 28 directly below the nozzle 34 is an interior chamber 50 that communicates with a bore 52 located in coaxial relation therewith. Parallel passages 54 and 56 also communicate with the interior chamber 50, the passage 54 having access to an exterior pipe 58 which is connected to a pressure responsive device generally indicated at 60. The passage 56 which is enclosed by a cap 62 is used to bleed the chamber 50 as required.

Slidably mounted in the bore 52 and extending inwardly into the chamber 50 is an air receiver generally indicated at 64. The air receiver 64 is formed with a reduced passage 66 that communicates with an enlarged passage 68, the enlarged passage 68 having direct communication with the interior chamber 50 at the bottom thereof. As illustrated in FIG. 1, the receiver 64 is of such a length as to extend for a substantial portion of the chamber 50; and as air from the nozzle 34 is directed into the receiver 64 and the interior chamber 50, the back pressure exerted on the receiver 64 from the chamber 50 will retain the receiver 64 in the uppermost position thereof within the bore 52. The passage 66 in the receiver 64 is located in direct vertical alignment with the passage 38 of the nozzle 34. It is seen that the nozzle 34 sprays the stream of compressed air 49 downwardly toward the passage 66 of the receiver 64; and if the strip material 32 is properly aligned in the channel 30, the air will be fully directed into the passages 66 and 68, chamber 50 and then outwardly of the base 28 by way of the passage 54.

In the normal operation of the punch press, the work material 32 is punched at the first or second work station to form a pilot opening 72. The pilot openings 72 are spaced along the strip material and may be used in aligning the strip during the punching operation. For purposes of operation of the present invention the pilot openings 72 are aligned at a selected station with the nozzle 34 and receiver 64 and are used to detect a misfeed of the work material. During the progressive feeding of the work material 32, the pilot openings 72 in the strip material are progressively aligned with the nozzle 34 and receiver 64 as indicated in FIG. 3; and the air under pressure is directed from the nozzle 34 through the aligned opening 72 and into the receiver 64. In normal operation and with a pilot opening 72 located in alignment with the nozzle 34 and receiver 64, a predetermined pressureis exerted on the pressure responsive device 60 that is operable to effect continued operation of the power press 10. For this purpose the pressure responsive device 60 includes a housing 75 in which an interior chamber 74 is formed that communicates with the conduit 58. Slidably located in the chamber 74 is a piston 76 to which a rod 78 is connected. A cap 80 is friction fitted into the end of the housing 75 and is formed with a bore in'which a spring 82 and an adjustment screw 84 are located. The adjustment screw 84 exerts pressure on the spring 82 to adjust the pressure that is necessary to move the piston 76 outwardly. A passage 86 is formed in the cap 80 for exhausting air that leaks between the housing walls and the piston 76. It is seen that when a predetermined amount of pressure is exerted on the piston 76 by compressed airdirected into the chamber 74 from the pipe 58, the rod 78 is forced outwardly and into engagement with a contact 88. of a switch 90. The switch 90 is located in a relay circuit 92 that is electrically interconnected to a power supply 94 and an emergency brake circuit 96. When the piston 76 is moved outwardly by a predetermined amount of pressure as exerted by the air received from the nozzle 34, the switch 90 is actuated to locate the power supply 94 in circuit therewith. The operating mechanism of the ram 12 is located in circuit with the power supply 94 and is thus operable to produce the operation of the device by cyclical movement of theram in a vertical direction to perform the punching operations. 1

If for any reason the work piece is improperly fed to the work station in the press 10, the pilot hole 72 located between the nozzle 34 and receiver 64 will be misaligned therewith, and the jet stream 49 will be deflected from the receiver 64, and only a portion of the stream will enter the receiver 64. As a result, the pressure of air as received in the chamber 74 of the pressure responsive device 60 will be reduced; and the piston 76 will not be moved outwardly sufficiently to close the switch 90. Accordingly, the circuit to the power supply 94 will be broken to discontinue operation of the operating means for the ram 12, and in addition the emergency brake circuit 96 will be energized to brake the operating mechanism for the ram 12 prior to the downstroke thereof.

It is understood that as the work piece 32 is fed through the work station of the press 10, the individual pilot openings 72 will be aligned with the nozzle 34 and and receiver 64; and although the nozzle and receiver can be located at any desired station in the press, they are preferably located at the second work station in the press.

In the operation of the punch press, and following a punching operation, the cyclical operation of the ram produces an upward movement thereof. As the pressurepad 24 lifts from engagement with the work material and the tool 32 is moved upwardly, the feed mechanism for the press (not shown) is operated to move the work material 32 in a feeding movement. Normally it is required that the jet of air from the nozzle 34 be received in the receiver 64 at the required pressure in order to retain the press in operation. However, since there is a period of movement of the work material in which the air jet is located between the openings 72 as the strip material is fed to the next station, the jet of air will not be received in the receiver 64, and it is necessary to provide a parallel circuit to maintain the press in operation until the feeding operation is completed. For this purpose, a probe 98 is provided and is mounted on the ram 12 through a bracket 100. The probe 98 defines a contact that is interconnected to an electrical lead 102 that is also located in circuit with the power supply 94. As the ram 12 is moved downwardly, the probe 98 engages the punch block 14 to establish a ground connection therewith and to locate the power supply 94 in circuit with the means for operating the ram 12. Since contact of the probe 98 with the punch block 14 occurs on the downward stroke of the ram, alignment of a pilot hole 27 in the work material 32 at the appropriate station and between the nozzle 34 and receiver 64 has already occurred. After the punching operation, and as the pressure pad 24 lifts off the work material 32, the feed operaton begins; and since the receiver 64 is blocked from the nozzle 34, contact of the probe 98 with the punch block 14 completes the circuit to the power supply 94 and movement of the ram 12 in an upward direction and feeding of the work material continues. As the ram 12 moves to an upward position, the probe 98 disengages from the punch block 14 and operation of the press 10 will continue only if the work material 32 has been moved properly and an opening 72 is in alignment with the nozzle 34 and receiver 64. If for any reason the work material 32 has been moved improperly or has become misaligned after the upward movement of the ram 12, the jet will be deflected by the misaligned opening in the work material, and the predetermined pressure that is required for movement of the piston 76 outwardly will not be exerted thereon, and the switch will remain open, whereby relay circuit 92 cannot be energized to connect the power supply to the operating mechanism for the ram 14. Since the ram 14 has not yet reached the upper position thereof when misfeeding occurs, it will be prevented from moving in a downstroke; and further, the emergency brake 96 will be energized to stop the operating mechanism just short of movement to the position that begins the downward stroke of the ram 14. Accord ingly, the ram 14 will be stopped on the upstroke and movement thereof downwardly cannot occur so long as the work piece 32 is misaligned or misfed. A reset ciruit is incorporated in the circuit and after the misfeed of the work material 32 has been corrected, a reset button is depressed and the operation of the apparatus continues as hereinabove described.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described.

What is claimed is:

l. A material misfeed detector for a power press, wherein the material is progressively transferred through a work station in said power press, comprising a base located at said work station and over which said work material is progressively transferred, a work tool located above said base and vertically movable relative thereto to perform the preselected work operation on said work material, operating means for producing the vertical movement of said work tool, and a safety device for detecting a misfeed of said work material and being operable to discontinue operation of said operating means so as to prevent damage to said work tool in striking the misfed work material, said safety device including a fluid discharge member located on one side of said work material at said work station and normally discharging a stream of compressed air therefrom through a preformed openingin said work material, a pressure responsive device responsive to a variation in pressure of the compressed air discharged from said fluid discharge member and when a misfeed of said work material occurs at said work station for discontinuing operation of said operating means, a contact located in circuit with said operating means and in parallel relation with said pressure responsive device, means for completing a circuit to said contact upon normal downward movement of the work tool during a work operation, said contact providing for feeding operation of said work material during upward movement of said work tool after a work operation.

2. A material misfeed detector as set forth in claim 1, a receiver located on the other side of said work material at said work station and in vertical alignment with said fluid discharge member, said receiver communicating directly with said fluid discharge member upon normal feed of said work material to said work station through the preformed opening in said work material for receiving the jet of compressed air therefrom, the pressure responsive device communicating with said receiver and being actuated in response to a predetermined pressure exerted thereon by the compressed air directed to said receiver for effecting operation of said operating means.

3. Apparatus as set forth in claim 2, said nozzle being located above said work material in a holder for said work tool and vertically movable therewith, said receiver being located in said base in vertical alignment with said nozzle.

4. Apparatus as set forth in claim 3, said base having a bore formed therein for receiving said receiver in sliding and floating relation, a chamber formed in said base and communicating with said bore, said receiver extending through said bore into the chamber located interiorly of said base and having a passage formed therein that communicates with said chamber and that is aligned with said nozzle for receiving the compressed air ejected therefrom, wherein the compressed air as directed into said passage is received in said chamber and retains said receiver in sliding and floating relation in said bore, and a conduit communicating with said chamber and directing the compressed air received from said passage to said pressure responsive device.

5. Apparatus as set forth in claim 4, said passage as formed in said receiver including an upper reduced portion that communicates with said nozzle, a lower enlarged portion that communicates with the chamber in said base, the reduced portion of the passage being confined within the bore in said base and the enlarged portion extending inwardly for a substantial portion of the interior chamber in said base.

6. Apparatus for automatically performing a preselected work operation on a work material that is progressively transferred through a work station in said apparatus, a base located at said work station and over which said work material is progressively transferred, a work tool located above said base and vertically movable relativethereto to perform the preselected work operation on said work material, and operating means for producing the vertical movement of said work tool, the improvement comprising a safety device for detecting a misfeed of said work material to said work station and being operable to discontinue operation of said operating means so as to prevent damage to said work tool in striking the misfed work material, said safety device including a nozzle located on one side of said work material at said work station and discharging a jet of compressed air therefrom, a receiver located on the other side of said work material at said work station and in vertical alignment with said nozzle, said receiver communicating directly with said nozzle upon normal feed of said work material to said work station through a preformed opening in said work material for receiving the jet of compressed air therein, a pressure responsive device communicating with said receiver and being actuated in response to a predetermined pressure exerted thereon by the compressed air directed to said receiver for effecting operation of said operating means, said pressure responsive device being responsive to a decrease in pressure when the jet of compressed air from said nozzle is deflected in its path through said work material to the receiver due to misfeed of said work material to interrupt the operation of said operating means, said nozzle being located above said work material in a holder for said work tool and vertically movable therewith, said receiver being located in said base in vertical alignment with said nozzle, a contact located in circuit with said operating means and in parallel relation with said pressure responsive device, and means for completing a circuit to said contact upon normal downward movement of the holder for said work tool during a work operation, said contact providing for feeding operation of said work material during upward movement of said work tool after a work operation.

7. Apparatus as set forth in claim 6, said contact being defined by an elongated probe that is adjustable in position relative to an electrical ground.

8. Apparatus as set forth in claim 3, said pressure responsive device being located in a relay circuit that is electrically interconnected to a circuit for an emergency brake, wherein said emergency brake is energized to discontinue operation of said operating means when said pressure responsive device is not moved sufficiently due to a decrease in pressure to said receiver.

9. A material misfeed detector as set forth in claim 1, said contact being defined by an elongated probe that is adjustable in position relative to an electrical ground.

* i I! t 

1. A material misfeed detector for a power press, wherein the material is progressively transferred through a work station in said power press, comprising a base located at said work station and over which said work material is progressively transferred, a work tool located above said base and vertically movable relative thereto to perform the preselected work operation on said work material, operating means for producing the vertical movement of said work tool, and a safety device for detecting a misfeed of said work material and being operable to discontinue operation of said operating means so as to prevent damage to said work tool in striking the misfed work material, said safety device including a fluid discharge member located on one side of said work material at said work station and normally discharging a stream of compressed air therefrom through a preformed opening in said work material, a pressure responsive device responsive to a variation in pressure of the compressed air discharged from said fluid discharge member and when a misfeed of said work material occurs at said work station for discontinuing operation of said operating means, a contact located in circuit with said operating means and in parallel relation with said pressure responsive device, means for completing a circuit to said contact upon normal downward movement of the work tool during a work operation, said contact providing for feeding operation of said work material during upward movement of said work tool after a work operation.
 2. A material misfeed detector as set forth in claim 1, a receiver located on the other side of said work material at said work station and in vertical alignment with said fluid discharge member, said receiver communicating directly with said fluid discharge member upon normal feed of said work material to said work station through the preformed opening in said work material for receiving the jet of compressed air therefrom, the pressure responsive device communicating with said receiver and being actuated in response to a predetermined pressure exerted thereon by the compressed air directed to said receiver for effecting operation of said operating means.
 3. Apparatus as set forth in claim 2, said nozzle being located above said work material in a holder for said work tool and vertically movable therewith, said receiver being located in said base in vertical alignment with said nozzle.
 4. Apparatus as set forth in claim 3, said base having a bore formed therein for receiving said receiver in sliding and floating relation, a chamber formed in said base and communicating with said bore, said receiver extending through said bore into the chamber located interiorly of said base and havinG a passage formed therein that communicates with said chamber and that is aligned with said nozzle for receiving the compressed air ejected therefrom, wherein the compressed air as directed into said passage is received in said chamber and retains said receiver in sliding and floating relation in said bore, and a conduit communicating with said chamber and directing the compressed air received from said passage to said pressure responsive device.
 5. Apparatus as set forth in claim 4, said passage as formed in said receiver including an upper reduced portion that communicates with said nozzle, a lower enlarged portion that communicates with the chamber in said base, the reduced portion of the passage being confined within the bore in said base and the enlarged portion extending inwardly for a substantial portion of the interior chamber in said base.
 6. Apparatus for automatically performing a preselected work operation on a work material that is progressively transferred through a work station in said apparatus, a base located at said work station and over which said work material is progressively transferred, a work tool located above said base and vertically movable relative thereto to perform the preselected work operation on said work material, and operating means for producing the vertical movement of said work tool, the improvement comprising a safety device for detecting a misfeed of said work material to said work station and being operable to discontinue operation of said operating means so as to prevent damage to said work tool in striking the misfed work material, said safety device including a nozzle located on one side of said work material at said work station and discharging a jet of compressed air therefrom, a receiver located on the other side of said work material at said work station and in vertical alignment with said nozzle, said receiver communicating directly with said nozzle upon normal feed of said work material to said work station through a preformed opening in said work material for receiving the jet of compressed air therein, a pressure responsive device communicating with said receiver and being actuated in response to a predetermined pressure exerted thereon by the compressed air directed to said receiver for effecting operation of said operating means, said pressure responsive device being responsive to a decrease in pressure when the jet of compressed air from said nozzle is deflected in its path through said work material to the receiver due to misfeed of said work material to interrupt the operation of said operating means, said nozzle being located above said work material in a holder for said work tool and vertically movable therewith, said receiver being located in said base in vertical alignment with said nozzle, a contact located in circuit with said operating means and in parallel relation with said pressure responsive device, and means for completing a circuit to said contact upon normal downward movement of the holder for said work tool during a work operation, said contact providing for feeding operation of said work material during upward movement of said work tool after a work operation.
 7. Apparatus as set forth in claim 6, said contact being defined by an elongated probe that is adjustable in position relative to an electrical ground.
 8. Apparatus as set forth in claim 3, said pressure responsive device being located in a relay circuit that is electrically interconnected to a circuit for an emergency brake, wherein said emergency brake is energized to discontinue operation of said operating means when said pressure responsive device is not moved sufficiently due to a decrease in pressure to said receiver.
 9. A material misfeed detector as set forth in claim 1, said contact being defined by an elongated probe that is adjustable in position relative to an electrical ground. 